After doing the usual web search with Google and Bing I found only sites claiming doing a scan with Microsoft Security Essentials of a file or directory from the command-line was not possible. Most sites just say it’s possible to initiate a quick or full scan or even update signatures from the command-line. But as Microsoft Security Essentials has real-time protection there is no need to scan manually (as a lot of us are used to) to make sure the file is scanned.

But on Windows 7 (x64 version confirmed) the tools in %ProgramFiles%\Microsoft Security Client contain some files that look promising. My first guess was to look into %ProgramFiles%\Microsoft Security Client\msseces.exe, but that program only pops-up the user-interface and worse case starts a default scan.

As Microsoft Security Essentials is able to scan manually (it has a explorer context menu, located in %ProgramFiles%\Microsoft Security Client\shell.ext.dll)

A far shot was to search for rundll32 to be used to fire the context menu but all I found was references to viruses and trojans doing the same (so not the best way to walk)

Finally I accidently fired up one of the other executables in %ProgramFiles%\Microsoft Security Client with a promising name (MpCmdRun.exe) with a switch –h and voila a long description with the answer tucked inside.